Technical Abstract:
Experiments testing the effects of climate change on plant productivity in a natural setting use open top chambers or Free-Air CO2 Enrichment (FACE) to elevate atmospheric CO2 concentrations. These experimental facilities are expensive to operate and rarely investigate temperature, an important component of climate change. In this study we used an existing gradient in atmospheric CO2 concentration and air temperature along a rural-urban transect to simulate short-term projections of climate change. We established four replicate plots of fallow agricultural soil in three locations: Baltimore Science Center (Urban), Carrie Murray Nature Center on the outskirts of Baltimore (Suburban) and an Organic Farm 50 km from Baltimore (Rural). The growth of plants and species composition of the plots was monitored over the growing season. The average daily CO2 concentration and air temperature of the rural and urban site over the growing season was 398 and 525 ppm (difference of 127 ppm) and 18.6 and 21.2 oC (difference of 2.6 oC). This compares well to the projections made by the Intergovernmental Panel on Climate Change (IPCC) of CO2 concentration (540-970 ppm) and air temperature increase (1.4-5.8 oC) by year 2100. The increase in CO2 concentration and air temperature between the rural and urban locations resulted in an increase in total plant biomass of 65% in 2002. In 2002, 96% of plant biomass was from two species and in 2003, 97% of plant biomass was from eight species. Total plant biomass decreased by 73% from 2002 to 2003. The large reduction in total plant biomass in 2003 may be because this was an exceptionally wet and cold year. These preliminary results indicate the rural-urban transect is a good model for climate change. This coming growing season above and below ground productivity will be measured and a carbon budget determined to see if this old field ecosystem will be a carbon sink or source with future estimates of atmospheric CO2 and air temperature.